Enhanced flight vision system

An Enhanced flight vision system (EFVS, sometimes EVS) is a system for imaging the external world from an aircraft, and to provide an image in which objects can be better detected. In other words, an EFVS is a system to provide and image which is better than unaided human vision. An EFVS includes sensors (one or many) such as a color camera, infrared camera or radar, and typically a display for the pilot, which can be a head-up display or head-down display. An EFVS may be combined with a synthetic vision system to create a combined vision system. [1]

History

Night vision devices for military personnel have been operational since the time of WW2. Their use has been adopted also by military pilots, mainly in rotary-wing aircraft (helicopters). The use of such devices has been suggested for use by commercial pilots since the 1970's, but it was not until 1999 that the first commercial, FAA certified system, was airborne. Still, the pilot could not use the system to lower an aircraft below the required natural vision limit. In 2004, the FAA published correction 91-281 to landing guidelines, which allowed pilots to use the visual display provided by an EFVS to lower down to 100 feet above the landing zone (if no other restrictions apply). This marks the first time an EFVS gave a concrete commercial advantage over unaided vision.

EVSs are traditionally based on a FLIR camera which gives a thermal image of the world, and captures the airport approach lights. However, since 2007 airports are switching to the more energy efficient LED lighting, which cannot be seen by traditional EVS. The new EVS designs are multispectral, to capture both LED lights and the thermal image of previous EVS generations.

Generation I EFVS

The first EVS comprised a cooled mid-wave infrared (MWIR) camera, or FLIR, by Kollsman. This, coupled to a HUD, was certified for flight with the Gulfstream V aircraft.

Airport LED transition and next generation EFVS

The Energy Independence and Security Act of 2007 prompted airports to switch from incandescent to LED lights, as a means of saving energy and costs. This has had a drastic effect on EVS design, since the previous generations are not able to see visible light LEDs. The solution proposed is to use multispectral imaging in order to capture both the different LEDs and regular lights, but also preserve the desirable aspects of previous generation EVS, namely, the thermal night landscape.

Future EVS designs focus on all-weather vision, which can be accomplished by intelligently fusing images and data from cameras operating in visible light, infrared, and millimeter-wave.

Functionality

The main purpose of an EVS is to permit takeoff, landing and taxiing in poor visibility conditions, where landing would not be safe otherwise. An EVS is certified for landing by the FAA only if it is combined with a HUD, in which case it is called an EFVS. [2]

The criterion for landing is known as decision height. ICAO defines Decision Height as "a specified altitude or height in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established." When a pilot in approaching the ground, they must see a visual reference to continue the approach. Visual references are for example the runway markings ("zebra stripes"), runway lighting, and approach lights (see [runway]] for more examples). If the pilot cannot see such a reference in the decision height, they must abort the landing, and then circle for a second approach or land elsewhere.

Above the decision height, the pilot uses mostly the aircraft displays. Below decision height, the pilot must look outside to identify visual references. In this stage the pilot alternates between looking at displays and looking out the window. This switching can be avoided if a HUD is installed to display information to the pilot while also looking out.

Decision Height

The decision height minimum is defined by ICAO for the following distinct categories. [3]

Alternatives to EVS-assisted landing

Instrument landing system

An Instrument landing system, or ILS, relies on radio signals to allow operation in any weather. For an ILS landing to be allowed, the system must be installed on the ground, and a suitably equipped aircraft and appropriately qualified crew are required. Not all airports and runways are suitable for ILS installation, because of terrain conditions (hills in the way of the signal, non-straight landing slope).

GPS-assisted landing

While the GPS has a very high inherent precision, the reliability is not high enough for landing. GPS signals may be intentionally jammed, or lose integrity. In such cases, it may take the GPS receiver a few seconds to detect the malfunction, which is too long for critical flight stages. GPS can be used to lower the decision height below the unaided threshold, down to cat I decision height minima, but not lower.

see also

references

  1. ↑ RTCA DO-341, Sep. 2012
  2. ↑ RTCA DO-315B (2012), "Minimum Aviation System Performance Standards (MASPS) for Enhanced Vision Systems, Synthetic Vision Systems, Combined Vision Systems and Enhanced Flight Vision Systems"
  3. ↑ ICAO Annex 14 - Aerodromes, 4th Ed., Vol.I, Ch.3 (July 2004)
This article is issued from Wikipedia - version of the Monday, April 25, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.